1. Field of the Invention
This invention relates to batteries and more particularly to substantially solid electrolytes for alkali-metal-ion batteries.
2. Description of the Related Art
Our society has come to rely on batteries to power a myriad of devices, including computers, cell phones, portable music players, lighting devices, as well as many other electronic components. Nevertheless, there is an ongoing need for further advances in battery technology. For example, there is still a significant need for economical batteries that can power automobiles or provide load-leveling capabilities for wind, solar, or other energy technologies. Furthermore, the “information age” increasingly demands portable energy sources that provide lighter weight, higher energy, longer discharge times, more “cycles”, and smaller customized designs. To achieve these advances, technologists continue to work to develop batteries with higher and higher energy densities while still providing acceptable safety, power densities, cost, and other needed characteristics.
Lithium-ion batteries have the potential to meet many of the above-stated needs. Lithium-ion batteries have a higher energy density than most other types of rechargeable batteries. They also operate at higher voltages than other rechargeable batteries—typically about 3.7 volts for lithium-ion compared to approximately 1.2 volts for nickel cadmium (NiCd) or nickel metal hydride (NiMH) batteries. This allows fewer cells to be used for a given application. Lithium-ion batteries also have a lower self-discharge rate than other types of rechargeable batteries—typically half that of nickel-based batteries. Lithium-ion batteries also exhibit good cycle life and have lower toxicity compared to other rechargeable systems.
Nevertheless, current lithium-ion batteries also have various limitations. For example, safety is a major issue as various lithium-ion chemistries maybe subject to thermal run-away and explosion. One of the primary reasons behind the hazard is the use of flammable organic solvents within typical lithium-ion batteries. Previous efforts to develop solid lithium-ion-conductive electrolytes have been largely unsatisfactory due to low conductivity. Other known solid electrolytes are unsatisfactory because of unacceptable physical characteristics. For example, lithium aluminum titanium phosphate (LATP), a lithium-ion-conductive ceramic, has good conductivity but by itself cannot be used as a separator because it is undesirably brittle and inflexible. Cracks or breakdown of the electrolyte separator may cause a catastrophic failure of the battery.
In view of the foregoing, what is needed is a robust, substantially solid electrolyte separator that can be used to reduce thermal run-away and flammability in alkali-metal-ion batteries. Ideally, such an electrolyte separator will be flexible, maintain its structural integrity even when very thin, and exhibit good ionic conductivity. Such an electrolyte separator may be used to produce a substantially solid state alkali-metal-ion (e.g., lithium-ion) battery, but may also be used advantageously in other types of batteries.